1. Field of the Invention
The present invention relates to a relatively thick base member to which an attachment member is attached and to an information storage apparatus having the base member as a carriage arm, the attachment member being composed of a relatively thin sheet member having a cylindrical boss section that projects from a surface of the sheet member and a path that passes through the sheet member and reaches the extreme end of the boss section.
2. Description of the Related Art
In an information storage apparatus, a carriage arm, which moves along a surface of a magnetic disc by receiving a drive force from an actuator, is ordinarily connected to a suspension arm through a spacer, the suspension arm having a magnetic head at the extreme end thereof that executes at least any one of recording and reproducing of information to and from a magnetic disc. When the carriage arm is connected to the suspension arm through the spacer, the suspension arm is attached to, for example, an end of the spacer by laser welding and the like, and the other end of the spacer is attached to the carriage arm. Heretofore, it is known to caulk one member to the other member as a method of strongly connecting the two members (refer to, for example, Japanese Patent Application Publication No. H55-1195). Further, the spacer is attached to the carriage arm by being caulked thereto (refer to, for example, Japanese Patent Application Publication No. 2001-353539). The technique disclosed in Japanese Patent Application Publication No. 2001-353539 employs a spacer having a cylindrical boss section projecting from a surface of a sheet member. The spacer disclosed in Japanese Patent Application Publication No. 2001-353539 has a path that passes through the sheet member and reaches the extreme end of the boss section. In contrast, the carriage arm disclosed in Japanese Patent Application Publication No. 2001-353539 has a through hole passing through the carriage arm in a thickness direction. Japanese Patent Application Publication No. 2001-353539 discloses a so-called ball caulking technique. According to the technique, the boss section is plastically deformed by causing a spherical body (ball) whose diameter is larger than that of the path to pass therethrough in the state that the boss section of the spacer is inserted into the through hole of the carriage arm, thereby the spacer is caulked to the carriage arm.
Incidentally, when the boss section is plastically deformed by a large amount in the passing-through direction of the spherical body, the sheet member is also pulled in the passing-through direction of the spherical body. Accordingly, there is a possibility that the suspension arm attached to the spacer inclines and the extreme end thereof is raised. To cope with the problem, the technique disclosed in Japanese Patent Application Publication No. 2001-353539 gives an ingenious idea to the spacer to suppress the large amount of plastic deformation of the boss section in the passing-through direction of the spherical body. That is, the plastic deformation of the boss section is suppressed by forming a hole in the vicinity of the boss section of the sheet member or by cutting out a part of the peripheral wall of the projecting boss section in a projecting direction.
However, since the thickness of the sheet member of the spacer is greatly smaller than that of the carriage arm, when the hole disclosed in Japanese Patent Application Laid-Ope No. 2001-353539 is formed, the strength of the spacer is lowered. Further, the strength of the boss section itself is lowered by the cut-out formed to the boss section. Accordingly, the spacer must be handled with extra caution to prevent the spacer from bending when it is assembled or to prevent breakdown of the boss section. Therefore a problem arises in that the handling property of the spacer is deteriorated.
This problem is not specific to the spacer attached to the carriage arm but is common to an attachment member attached to a base member. Accordingly, there is a requirement for a technique that can suppress a large amount of plastic deformation of a boss section in the passing-through direction of a spherical body on the side of a base member whose thickness is larger than that of a sheet member of a spacer.